The objectives of this research are to establish the mechanism by which monovalent cations are taken up and extruded by heart mitochondria and the physiological significance of the flux of K ion and Na ion across the mitochondrial membrane. Experiments to date seem best explained by the presence of two opposing pathways for cation flow, a cation/H ion exchanger which is responsible for cation extrusion at the expense of delta pH and a uniport pathway which promotes electrophoretic cation entry in response to a negative interior membrane potential delta psi. A combination of osmotic volume changes, isotopic flux determinations, and specific ion electrode responses will be used to confirm the existence of these two putative cation transport pathways, establish the number of components of each type which are involved and the distribution of such components in mitochondria from various sources, and determine the factors which control or regulate the activity of these transporters to prevent futile influx-efflux cycling of cations. Stoichiometry of exchanges, cation selectivity, inhibitor profiles, and kinetic parameters for mitochondrial cation movements will be established under conditions which favor transport first by exchange and then by uniport pathways. These properties of the transport components will be used to establish criteria for the isolation and reconstitution of active fractions into liposomes to establish the molecular bases of transport activity. Heart mitochondria and isolated heart cells will be used to examine the effects of specific alterations in cell metabolism on monovalent cation flux across the mitochondrial membrane and to determine whether such ion fluxes in turn can alter or regulate metabolic pathways in the cytosol or matrix compartments of the cell either directly or indirectly.